The electrodes concerned are conventional electrodes which consist wholly of material consumed within a furnace environment, such as graphite.
In electric arc furnaces of typical size, each fitted with at least three electrodes of the type concerned, it is generally necessary at least once each operating day to refit at least one electrode for further furnace operation by the mounting of a new active electrode section. This refitting is often performed manually. Where a conventional electrode is being refitted, nippling up of a new active electrode section to the top end of a substantially spent electrode shank is accomplished by employing a lifting appliance such as a shop crane, to move a new electrode section over the electrode shank clamped in an electrode holder upon the arc furnace. The new electrode section is lowered such as by a screw nipple already mounted on lower end of the new section, so that the screw nipple of the new electrode section is inserted into a bore in the top end of the electrode shank being refitted. Then, using clamps, the nippling up of the new electrode section is carried out by manually threading the new section onto the top end of the electrode shank.
Such a nippling up process counts among its disadvantages the operators having to work on the cover of the arc furnace, where they are exposed to great heat, and to carbon monoxide and carbon dioxide gases escaping from the furnace for the duration of the work, generally several minutes. In addition proper joining of the new section to the rest of the electrode shank is dependent on the skills of the operators as to correct connection, with a required initial tension. The initial tension between the newly connected electrode sections has a significant influence on the electrical transfer resistance between the electrode sections, and thus on the functioning and energy consumption of the electrode.
To alleviate such difficulties, several means for nippling up conventional electrodes already have been proposed.
A known device as shown in German Patent OS 16 90 556 comprises two cylinders coaxially arranged one inside the other. The inner cylinder is rotatable by a drive relative to the outer cylinder. The inner cylinder has on its lower end chucks radially pressable onto the lower end of an electrode section to be refitted by being nippled up. The outer cylinder can be supported employing torsional forces in an inserted position against the electrode holder which is fixed on the furnace.
Such a device makes the mechanical nippling up of an electrode section on an electrode clamped in an electrode holder fixed on a furnace possible. Thus there is no need for workers to be upon the cover of a furnace which is in operation which today is scarcely reasonable in the light of modern regulations concerning work conditions.
However such a device described is relatively costly. The device includes two electric motors; one is located above the inner cylinder intended to clamp the electrode section by an axially relative motion between the two cylinders; the second motor is arranged not far from the lower end of the device on the outer cylinder and rotates the inner cylinder via a worm gear for the nippling up process. Such a configuration results not only in a very substantial height for the device, but also in a large diameter adjacent the furnace. The large diameter can be very disadvantageous to operability of the device. When clamping an electrode section, the inner cylinder, designed as a clamping bush is displaced in the direction of its longitudinal axis against a surrounding conical ring, so that the clamping elements, at least at the start of the clamping motion, may mechanically damage the electrode section; this may lead to later crack formation in the electrode section during use in a furnace.
To overcome these disadvantages, the known device has been further developed as shown by German Pat. Publication AS 24 18 688 to provide between the two cylinders a third, coaxially arranged cylinder (intermediate cylinder) which for clamping of an electrode section to be nippled up is displaceable in the direction of its longitudinal axis by a threaded nut rotatable employing a motor driven toothed or chain-drive arranged adjacent the upper portion of the outer cylinder. Rotation of the threaded nut effects the rotation of the intermediate cylinder. To nipple up the electrode section, a detent securing the inner cylinder against rotation during the clamping process is released.
Because of this intermediate cylinder design, such a device has near the furnace an outer diameter only slightly exceeding that of the electrode. In addition, clamping and nippling up is done by a common motor located adjacent the head of the device resulting in a shortening of the height of the device. As before such devices are still relatively large, since the new electrode section being nipped up is clamped at its lower end so that the height is still substantially greater than the length of the new electrode section. A major disadvantage in the case of such device is that three cylinders are provided each having the required length, making the device both costly in materials and correspondingly heavy.
In both these prior devices a common drawback is that the new electrode section is grasped by a chuck causing a complicated design of the overall device and complicating the acceptance of a new electrode section in the nippling up device since the nippling up device has to be exactly axially aligned relative to the electrode section.
A further known nippling up device is shown in German Pat. No. OS 23 38 741. An electrode section to be connected with the electrode is firmly clamped in a holder ring rotatable and vertically adjustable against the electrode holder on the arc furnace. For this purpose a support frame is provided having a support ring guided thereon and an interposed suspension. The support ring carries a drive means and a holder ring suspended on the support ring, the holder ring being equipped with peripherally hydraulically acturated clamping devices for holding the electrode portion in its interior in driven relationship axially with an interposed ring gear secured on the holder ring and rotatable against the support ring, corresponding to the pitch of the nipple connection between the electrode and the electrode section. The suspension is displaceable transversely to the longitudinal axis of the electrode and the support frame is configured as a movable unit having relevant components equipped with guidance parts, by means of which the support frame can be connected in a precisely defined position relative to the electrode holder. After completion of the nipple connection between the electrode and the electrode section mounted thereon, the nippling up device can, after release of the clamping means of the holder ring, be lifted from the electrode holder by a lifting appliance and used elsewhere.
But such a device also has a relatively complicated design caused, on one hand by a costly clamping means and on the other hand by the need for a special support frame for the support ring and a holding ring, whereby the diameter of the device perpendicularly to the axis of the electrode is substantially increased, complicating operability of the device.
All these prior nippling up devices grasp the electrode section by its shell employing a clamping means or the like. Since the electrodes consist of a material such as graphite which is sensitive to certain mechanical stresses, there is a danger that the clamping means may damage the surface of the electrode by formation of furrows, notches or the like. If such a damaged surface of the electrode section engages the electrical contact jaws of the furnace, because of the damage, the electrical transfer efficiency will be reduced resulting in an increased electrical current consumption and/or a certain fall in the performance of the electrode.